Dual wavelength photon sieves

Abstract

Photon sieves (PSs) are diffractive lenses with an array of pinholes that are capable of focusing light with either short, visible, or long wavelengths. PSs were fabricated using electron-beam lithography to pattern opaque silver films on a glass substrate (3 mm diam, 51.7 mm focal length). The size and spacing of pinholes was varied to create single and dual-wavelength PSs to focus 500 and/or 600 nm light, and the pinholes for the dual wavelength design were arranged in sectors, concentric with one another, or randomly. Single wavelength PSs produced focused images of a 100 µm source aperture with full width at half maximum (FWHM) of ~100 µm and high relative intensities at the design wavelength. Chromatic aberration resulted in no focused image and very low intensities when monochromatic light was 100 nm from the designed wavelength. Dual wavelength PSs produced focused images of the 100 µm source aperture with FWHMs of ~100 µm but lower relative intensities at both design wavelengths of 500 and 600 nm. The background “secondary maxima” were higher for dual wavelength designs, especially when the PS was illuminated by white light. The FWHM was smaller and the intensities higher for the random or concentric dual wavelength designs as compared to the sector design.